Indwelling heat exchange catheter and method of using same

ABSTRACT

A catheter is adapted to exchange heat with a body fluid, such as blood, flowing in a body conduit, such as a blood vessel. The catheter includes a shaft with a heat exchange region disposed at its distal end. This region may include hollow fibers which are adapted to receive a remotely cooled heat exchange fluid preferably flowing in a direction counter to that of the body fluid. The hollow fibers enhance the surface area of contact, as well as the mixing of both the heat exchange fluid and the body fluid. The catheter can be positioned to produce hypothermia in a selective area of the body or alternatively positioned to systemically cool the entire body system.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates generally to apparatus and methods forproducing heat exchange with body tissue, and more specifically tomethods and apparatus for the hypothermic treatment of a body fluid in abody conduit.

[0003] 2. Discussion of the Prior Art

[0004] Many of the advantages of hypothermia are well known. By way ofexample, it has been found particularly desirable to lower thetemperature of body tissue in order to reduce the metabolism of thebody. In stroke, trauma and several other pathological conditions,hypothermia also reduces the permeability of the blood/brain barrier. Itinhibits release of damaging neurotransmitters and also inhibitscalcium-mediated effects. Hypothermia inhibits brain edema and lowersintracranial pressure.

[0005] In the past, hypothermic treatment has been typically addressedsystemically, meaning that the overall temperature of the entire bodyhas been lowered to achieve the advantages noted above. This has beenparticularly desirable in surgical applications where the reducedmetabolism has made it possible to more easily accommodate lengthyoperative procedures. An example of this systemic approach includescatheters for transferring heat to or from blood flowing within apatient's vessel, as disclosed by Ginsburg in U.S. Pat. No. 5,486,208. Aclosed loop heat exchange catheter is also disclosed by Saab in U.S.Pat. No. 5,624,392. A cooling device for whole-body hyperthermia thatutilizes the circulatory system of the body is known to be moreefficient since the entire volume of the body is constantly perfusedwith the cold fluid at a capillary level.

[0006] Likewise, various other means of cooling the body have been triedwith cooling blankets, ice water bladder lavages, ice baths, esophagealcatheters and their associated methods. All of these devices require aconsiderable time to cool the body since the primary heat transferoccurs through the skin or the skull. A more efficient body coolingdevice that can quickly cool and accurately control the body temperatureis required.

SUMMARY OF THE INVENTION

[0007] A heat exchange catheter and method of operation are included inthe present invention. The method is adapted to produce hypothermia orhyperthermia, typically in a selected portion of the body withoutsubstantially varying the temperature of the remaining portions of thebody. The selected body portion will usually be associated with a bodyconduit which conveys a body fluid to the selected body portion. Ofparticular interest are the organs of the body which are commonlynourished and maintained by a flow of blood in the arterial system. Forexample, a flow of blood is introduced to the brain through the carotidartery. Of course the temperature of this blood is usually at the normalbody temperature.

[0008] By positioning a heat exchange catheter in the body conduit, heatcan be added to or removed from the body fluid to heat or cool theselected body portion. For example, the heat exchange catheter can bedisposed in the carotid artery where the arterial blood flowing to thebrain can be cooled. The flow of cooled blood to the brain reduces thetemperature of the brain thereby resulting in cerebral hypothermia.Importantly, this temperature reduction occurs primarily and selectivelyin the brain; the remaining portions of the body maintain a generallynormal body temperature. In accordance with this method, the selectedbody portion, such as the brain, can be cooled thereby providing theadvantages associated with hypothermia for this body portion. Theremainder of the body, such as the portions other than the brain, do notexperience the reduction in temperature. Furthermore, the invention isintended to remotely alter temperature in a region other than the pointof introduction into the body. This is different than devices intendedfor systemic temperature control.

[0009] Several factors are of interest in effecting heat transfer in aheat exchanger. These factors include, for example, the convection heattransfer coefficient of the two fluids involved in the heat exchange, aswell as the thermal conductivity and thickness of the barrier betweenthe two fluids. Other factors include the relative temperaturedifferential between the fluids, as well as the contact area andresidence time of heat transfer. The Reynolds number for each fluidstream affects boundary layers, turbulence and laminar flow.

[0010] Notwithstanding the need for localized hypothermia, there willalways be those procedures which call for systemic hypothermia. Many ofthe advantages associated with the present invention will greatlyfacilitate those procedures, for example, by decreasing the number andcomplexity of operative steps, increasing the heat transfer capacity ofthe device, and addressing other concerns such as the formation of bloodclots.

[0011] In one aspect of the invention a catheter is provided with anelongate configuration, a proximal end and a distal end. An outer tubehaving a first lumen extends between the distal end and proximal end ofthe catheter, and an inner tube having a second lumen is disposed withinthe first lumen of the outer tube. Portions of the inner tube define afirst flow path extending along the second lumen, while portions of thetubes define a second flow path extending between the first tube and thesecond tube. A plurality of hollow fibers provide fluid communicationbetween the first and second flow paths, and a heat exchange fluid isdisposed in the hollow fibers to cool the fibers.

[0012] In another aspect of the invention, a method for making a heatexchange catheter includes the steps of providing first and second tubeshaving first and second lumens, respectively. A plurality of hollowfibers are connected between a first flow path extending along thesecond lumen and a second flow path extending along the first lumenoutwardly of the second tube. The method further comprises the step ofinsuring that the second tube is axially or rotationally movablerelative to the first tube in order to vary the configuration of thehollow fibers.

[0013] In a further aspect of the invention, a method for operating aheat exchange catheter includes the steps of inserting into a bodyconduit the catheter with an inner tube disposed within an outer tubeand defining a first flow path interiorly of the inner tube and secondflow path between the inner tube and the outer tube. This insertedcatheter also includes a plurality of hollow fibers disposed in fluidcommunication with the first and second flow paths. The method furtherincludes steps for creating a flow of heat exchange fluid through thefirst and second flow paths, and moving the inner tube relative to theouter tube to change the profile of the hollow fibers.

[0014] In a further aspect of the invention, a heat exchange catheterincludes an elongate shaft with first portions defining an inlet lumenand second portions defining an outlet lumen. A first manifold isdisposed in fluid communication with the inlet lumen and a secondmanifold disposed in fluid communication with the outlet lumen. Aplurality of hollow fibers are disposed between the manifolds in fluidcommunication with the inlet and outlet lumens. The catheter is adaptedto receive a heat exchange fluid and to direct the heat exchange fluidthrough the hollow fibers to exchange heat through the hollow fibers.

[0015] In still a further aspect of the invention, a catheter is adaptedto exchange heat with the body fluid flowing in a first directionthrough a body conduit. The catheter includes a shaft having an inputlumen and an output lumen. A plurality of hollow fibers define a heatexchange region and collectively define an output surface of the heatexchange region. The input lumen of the shaft is coupled to the hollowfibers at a first location while the output lumen of the shaft iscoupled to the hollow fibers at a second location disposed in the firstdirection from the first location.

[0016] Another aspect of the invention includes a method for exchangingheat with a body fluid in a body conduit. In this case, a catheter isprovided with a plurality of hollow heat exchange fibers extending influid communication with an inlet lumen and an outlet lumen of thecatheter. The heat exchange fibers collectively define a first cavity inheat transfer relationship with a body fluid in a body conduit.

[0017] In an additional aspect of the invention, an operative area ofthe catheter is sized and configured for disposition in a vesselcontaining blood. The operative area is adapted to perform apredetermined function, and the blood in the vessel has a tendency toform clots. In this aspect of the invention, the catheter is providedwith a snare disposed relative to the operative area and being operablefrom a proximal end of the catheter to move from a low-profile statefacilitating insertion of the catheter, to a high-profile statefacilitating the capture of blood clots.

[0018] In still a further aspect of the invention, a heat exchangecatheter is adapted for cooling the blood of a patient. The catheterincludes a heat exchange region with a plurality of fibers each having ahollow configuration. A heat exchange fluid is disposed in the hollowfibers to cool the fibers and a coating is disposed on the outer surfaceof the fibers to inhibit formation of blood clots.

[0019] These and other features and advantages of the invention will bebetter understood with a description of the preferred embodiments of theinvention and reference to the associated drawings.

DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1 is side elevation view of a patient lying in a proneposition with a heat exchange catheter of the present inventionappropriately inserted to facilitate hypothermic treatment of thepatient's brain;

[0021]FIG. 2 is an enlarged side elevation view showing the vasculatureassociated with the patient's head and brain;

[0022]FIG. 3 is a perspective view partially in section of a heatexchange region of the catheter;

[0023]FIG. 4 is an enlarged axial cross section view of a plurality ofballoons disposed in the heat exchange region of the catheter;

[0024]FIG. 5 is a radial cross section view of the catheter taken alonglines 5-5 of FIG. 4;

[0025]FIG. 6 is a radial cross section view similar to FIG. 5 of afurther embodiment of the catheter;

[0026]FIG. 7 is a perspective view of a further embodiment of thecatheter wherein multiple balloons are provided with a longitudinalconfiguration;

[0027]FIG. 8 is a radial cross section view taken along lines 8-8 ofFIG. 7;

[0028]FIG. 9 is an axial cross section view taken along lines 9-9 ofFIG. 7;

[0029]FIG. 10 is a perspective view of the catheter illustrated in FIG.3 further illustrating structures which can facilitate mixing and heatexchange;

[0030]FIG. 10A is a perspective view of an embodiment of the catheterhaving a distal end with a pigtail configuration;

[0031]FIG. 10B is a perspective view of the catheter illustrated in FIG.10A with the distal end straightened by a stylet 174 to facilitateinsertion of the catheter;

[0032]FIG. 11 is a schematic view of an embodiment including a heatpipe;

[0033]FIG. 12 is a schematic view, partially in section, of a heat pipeadapted for use in the embodiment of FIG. 11;

[0034]FIG. 13 is a top plan view of carotid artery branch illustratingone method of operation associated with the catheter;

[0035]FIG. 14 is a top plan view similar to FIG. 13 and showing afurther method of operation with the catheter;

[0036]FIG. 15 is a top plan view of the carotid branch similar to FIG.13 and showing a further method of operating a heat exchange catheter;

[0037]FIG. 16 is a radial cross section of the catheter taken alonglines 16-16 of FIG. 15;

[0038]FIG. 17 is an axial cross section view of a further embodiment ofthe invention including hollow fibers in the heat exchange region;

[0039]FIG. 18 is a side elevation view similar to FIG. 17 andillustrating the hollow fibers in a compacted configuration; and

[0040]FIG. 19 is an axial cross section view of the catheter of FIG. 17operatively disposed and configured to permit the hollow fibers to floatand undulate within a blood stream.

[0041]FIG. 20 is a side elevation view partially in section andillustrating a further embodiment of the catheter of the presentinvention;

[0042]FIG. 21 is a radial cross-section view taken along the lines 21-21of FIG. 20;

[0043]FIG. 22 is an axial cross-section view of the proximal end of thecatheter illustrated in FIG. 20;

[0044]FIG. 23 is an axial cross-section view of the distal end of afurther embodiment illustrating the heat exchange region in alow-profile state;

[0045]FIG. 24 is an axial cross-section view similar to FIG. 23 andillustrating the heat exchange region in a high-profile state;

[0046] FIGS. 25-27 illustrate a preferred method for manufacturing theheat exchange region of a hollow fiber embodiment of the cavity;

[0047]FIG. 25 is a top plan view of a mat formed of the heat exchangefibers;

[0048]FIG. 26 is a perspective view illustrating formation of the mataround the distal ends of the concentric tubes;

[0049]FIG. 27 is a side elevation view illustrating attachment of themat assembly to an outer tube of the catheter;

[0050]FIG. 28 is a top-plan view of a patient illustrating portions ofthe blood circulatory system;

[0051]FIG. 29-33 illustrate a method for introducing the catheter of thepresent invention;

[0052]FIG. 29 is a side elevation view illustrating a introducing sheathin a first position removed from the heat exchange region;

[0053]FIG. 30 is a side elevation view illustrating the sheath in asecond position over the heat exchange region of the catheter;

[0054]FIG. 31 is a side elevation view illustrating the catheter andsheath being inserted into an introducer;

[0055]FIG. 32 is a side elevation view illustrating the catheter furtherinserted with the sheath maintained in the introducer;

[0056]FIG. 33 is a side elevation view illustrating removal of thesheath to the first position;

[0057]FIG. 34 is a perspective view of a further embodiment of thecatheter including a distal clot filter in a low-profile state;

[0058]FIG. 35 is a perspective view illustrating the catheter of FIG. 34with the clot filter in a high-profile state;

[0059]FIG. 36 is a perspective view of a catheter with a clot filterhaving free ends and automatically deployable to a high-profile state;and

[0060]FIG. 37 is a side elevation view of the catheter of FIG. 36 with asheath maintaining the clot filter in a low-profile state.

DESCRIPTION OF THE PREFERRED EMBODIMENTS AND BEST MODE OF THE INVENTION

[0061] A heat exchange catheter is illustrated in FIG. 1 and designatedgenerally by the reference numeral 10. The catheter 10 is operativelydisposed with respect to a body 12 of a patient having a groin 14, ahead 16, and a brain 18. More specifically, the catheter 10 can beinserted percutaneously through a puncture or surgical cut down at thegroin 14, and into the femoral artery 21. Following this initialintroduction, the catheter 10 can be moved through the femoral artery 21and the aortic arch 23, into the common carotid artery 25 bestillustrated in FIG. 2. This common carotid artery 25 divides at acarotid branch 27 into an external carotid artery 30, which primarilysupplies blood 1 to the face of the patient, and an internal carotidartery 32, which primarily supplies blood to the brain 18 of thepatient.

[0062] In the concept of this invention, the brain 18 is merelyrepresentative of a portion of the body 12 of the patient, and thearteries 21, 25, 30 and 32 are merely representative of conduits whichsupply a body fluid, such as blood, to a selected portion of the body12, such as the brain 18. By cooling the body fluid, such as blood 31,in the body conduit, such as the artery 32, the specific body portion,such as the brain 18, can be selectively cooled without significantlyaffecting the temperature of the remaining portions of the body 12.

[0063] Selective hypothermic treatment of the brain 18 is initially ofparticular interest as it captures the advantages of hypothermia duringoperative procedures associated with the brain 18 without also capturingthe disadvantages of hypothermia with respect to other areas of the body12. Thus, a surgeon operating to treat an aneurysm in the brain 18, forexample, can initially cool the brain 18 in order to facilitate thatprocedure. This selective hypothermia will be particularly appreciatedin those surgical procedures which are primarily directed to the brain18. Procedures such as stroke, trauma, and other brain related injurieswill also benefit up to and during from this selective hypothermiatreatment.

[0064] A preferred embodiment of the catheter 10 of the presentinvention is illustrated in FIG. 3 and 4. From this perspective view, itcan be seen that the catheter 10 includes a shaft 40 having an axis 41which extends between a proximal end 43 and a distal end 45. Whenoperatively disposed, a heat exchange region 47 at the distal end 45 isoperatively disposed within the body 12, and a hub 50 at the proximalend 43 is disposed outside of the body 12. Within the shaft 40, aplurality of lumens 52 and 54 extend in fluid communication with the hub50 and the heat exchange region 47.

[0065] A preferred embodiment of the heat exchange region 47 isillustrated in greater detail in FIG. 4 where three balloons 56, 58 and61 are individually, separately and axially disposed along the shaft 40.It will be appreciated that although the illustrated embodiment includesthree balloons, a single balloon or double balloon embodiment may offerfurther advantages in a particular procedure. All of the balloons 56, 58and 61 are illustrated to have a significantly larger diameter than theshaft 40. This may not be the case in other embodiments. Morespecifically, it may be desirable to maximize the dimension of the shaft40 in order to facilitate flow of the heat exchange fluid. This willalso minimize the volume of fluid in the balloon and promote a morerapid heat exchange. In one such embodiment, the diameter of the shaft40 is in a range between 50 and 90 percent of the diameter of theballoons 56, 58 and 61.

[0066] Each of the balloons 56, 58 and 61 can be formed from a piece ofsheet material 62, 64 and 66 which is bound or otherwise fixed to theshaft 40 to form a cavity 63, 65 and 67, respectively. An inlet hole 70provides fluid communication between the lumen 54 and the cavity 63 ofthe balloon 56. Similar inlet holes 72 and 74 are provided for theballoons 58 and 61. In a like manner, an outlet hole 76 can be formed inthe wall of the shaft 40 to provide fluid communication between thelumen 52 and the cavity 63 of the balloon 56. Similar outlet holes 78and 81 are provided for the balloons 58 and 61, respectively. With thisstructure, it can be seen that the lumen 54 functions primarily as aninlet lumen for a heat exchange fluid which is illustrated generally asa series of arrows designated by the reference numeral 85.

[0067] Initially, the heat exchange fluid 85 is introduced through thehub 50 (FIG. 3) and into the inlet lumen 54. From the lumen 54, the heatexchange fluid 85 passes through the inlet holes 70, 72, 74 and into therespective balloon cavity 63, 65 and 67. The heat exchange fluid 85 thenpasses into the outlet hole 76, 78, 81 and into the outlet lumen 52 andthe hub 50 to regions exterior of the catheter 10.

[0068] After the heat exchange fluid 85 is remotely cooled, it iscirculated through the balloon cavities 63, 65 and 67 to provide a coldtemperature fluid on the inner surface of the sheet materials 62, 64 and66 which form the walls of the balloons 56, 58 and 61, respectively.With a body fluid, such as blood 31, flowing exteriorly of the balloons56, 68 and 61, heat transfer occurs across the sheet materials 62, 64and 66, respectively.

[0069] It can be appreciated that this circulation of the heat exchangefluid 85 can be formed with any structure of the shaft 40 which providestwo lumens, such as the lumens 52 and 54, each of which can have accessto the balloon cavities, such as the cavities 63, 65 and 67. In oneembodiment of the shaft 40 illustrated in FIG. 5, a septum 90 isprovided which separates the cylindrical shaft 40 into two equally sizedlumens 52 and 54. In the embodiment of FIG. 6, the cylindrical shaft 40is provided with a cylindrical septum 92 which provides the lumen 54with a circular cross section and the lumen 52 with a moon-shaped crosssection. In such an embodiment, the lumen 54 must be defined off-axisfrom the shaft 40 in order to have access to the balloon cavities, suchas the cavity 63.

[0070] One of the advantages of a multiple balloon embodiment of thecatheter 10 is that the flow and temperature of the heat exchange fluid85 can be more easily controlled along the entire length of the heatexchange region 47. Realizing that the heat exchange fluid 85 will becoolest prior to entering into a heat exchange with the blood 31, andwarmest after that heat exchange, one can advantageously control notonly the velocity and volume of flow, but also the direction of flowwithin each discrete balloons 56, 58 and 61. Another advantage of amultiple balloon design is the ability of the catheter to bend and flexwhen placed in a curved vasculature. Single balloon designs would berigid, stiff and inflexible by comparison.

[0071] In order to facilitate the maximum heat exchange between thefluid 85 and the blood, it is desirable to provide a balanced flow ofthe heat exchange fluid 85 along the entire length of the heat exchangeregion 47. In the embodiment illustrated in FIG. 4, efficient heattransfer is facilitated by countercurrent flow where the heat exchangefluid 85 is directed to flow counter to the flow of the blood 31. Tothat end, the inlet holes 70, 72 and 74 are positioned distally of theoutlet holes 76, 78 and 81, respectively. As the blood 31 flows distallyalong the outer surface of the catheter 10, this relative position ofthe inlet holes and outlet holes causes the heat exchange fluid to flowin the opposite direction, proximally in each of the balloons 56, 58 and61.

[0072] The amount of flow within each of the balloons 56, 58 and 61 canalso be controlled by the size of the inlet holes 70, 72, 74 and outletholes 76, 78 and 81. In a preferred embodiment, this flow control isprovided solely by the inlet holes 70, 72 and 74; the outlet holes 76,78 and 81 are sized larger than their respective inlet holes so thatthey offer little resistance to flow. In this embodiment, the inletholes 70, 72 and 74 are sized to be progressively smaller from thedistal end 45 to the proximal end 43. Thus the hole 70 is larger thanthe hole 72 which is larger than the hole 74. As a result, theresistance to the flow of heat exchange fluid 85 in the most distalballoon 56 is less than that in the most proximal balloon 61. Thisensures that the coolest heat exchange fluid 85 is shared equally amongall of the balloons 56, 58 and 61 regardless of their position along theshaft 40. In an embodiment wherein the flow is controlled by the outletholes 76, 78 and 81, these holes can also be provided with a relativelyreduced size from the distal end 45 to the proximal end 43. With any ofthese structures, a more balanced flow of the heat exchange fluid can beachieved in order to facilitate the highest degree of heat exchangealong the entire heat exchange region 47. Alternatively, the flow ofheat exchange fluid can also be balanced by providing the holes 76, 78and 81 with non-circular configurations. For example, these holes may beformed as longitudinal slits extending axially of the catheter.

[0073] A further embodiment of the invention is illustrated in FIG. 7wherein a single sheet of material 101 is used to form separate anddistinct individual balloons, two of which are designated by thereference numerals 103 and 105. As opposed to the radial balloons 56, 58and 61 of the previous embodiment, the balloons 103 and 105 extendaxially along the surface of the shaft 40. For example, the balloons 103and 105 form individual balloon cavities 107 and 110, respectively,which extend from a distal end 112 to a proximal end 114.

[0074] This embodiment of the catheter containing the axial balloons 103and 105 may include a shaft 40 with a slightly different configuration.As best illustrated in FIG. 9, the shaft 40 may include an outer tube121 having an outer surface to which the sheet material 101 is attachedand within which is disposed a distal sealing plug 123. An inner tube125, which can be disposed coaxially with the outer tube 121, has aninner lumen 127 and defines with the outer tube 121 an outer lumen 130.A pair of inlet holes 132 and 134 provide flow fluid communicationbetween the inner lumen 127 and the balloon cavities 107 and 110,respectively. Similarly, a pair of outlet holes 136 and 138 providefluid communication between the balloon cavities 107 and 110 and theouter lumen 130, respectively. An inner plug 141 disposed between theinner tube 125 and outer tube 121 to seal the outer lumen 130 betweenthe inlet holes 132, 134 and outlet holes 136, 138. For the reasonspreviously noted, a preferred embodiment has inlet holes 132, 134 whichare disposed distally of and sized smaller than the outlet holes 136,138, respectively. This orientation will provide countercurrent flow ina catheter 10 which is inserted downstream into an artery such as thecarotid artery 25.

[0075] Embodiments which are intended to maximize heat transfer willtake advantage of the fact that heat exchange is enhanced when either,or both, the body fluid or the heat exchange fluid is provided with wellmixed flow. Mixing can be enhanced by providing irregular surfaces nextto which either of these fluids flow. For example, with reference toFIG. 4, it will be noted that a spring 150 can be disposed around theshaft 40 inside each of the balloons, such as the balloon 61. In thisembodiment, the spring 150 upsets the laminar flow of the heat exchangefluid 85 thereby producing the desired mixing of this fluid. Otherstructures can be positioned within the cavities formed by the balloons56, 58 and 61.

[0076] Mixing can also be enhanced within the body fluid which flowsalong the outer surface of the catheter 10. In this case, the multipleradial balloon embodiment illustrated in Figure 4 is of advantage aseach of the balloons 56, 58 and 61 represents a peak and defines withthe adjacent balloon a valley along which the blood 31 flows. Thisseries of peaks and valleys also upsets the laminar flow of the bodyfluid. Mixing of the body fluid can also be enhanced by providing otherstructures along the outer surface of the sheet material 62, 64 and 66which form the balloons as well as any exposed areas of the shaft 40 inthe heat exchange region 47. By way of example, a multiplicity ofgranules 145 can be adhered to the outer surface of the radial balloons56, 58 and 61 or the axial balloons 103 and 105 as illustrated in FIG.9. Ridges can also be provided along these surfaces.

[0077] With some body fluids, it may be desirable to inhibit turbulentflow and facilitate laminar flow. This may be true for example in thecase of blood where undesirable hemolysis may occur in response toincreased turbulence. Such an embodiment might be particularly desirablefor use with radial balloons where an outer balloon 152 would promotelaminar flow by reducing the height differential between the peaks andvalleys defined by the balloons 56, 58 and 61. This outer balloon 152 isbest illustrated in FIG. 10. To further promote laminar flow, the outersurface of any structure in the heat exchange region 47 can be providedwith a coating 154, such as a hydrophilic or a hydrophobic coating tomodify the boundary layer. Thus the outer surface of the shaft 40 aswell as the outer surface of any of the balloons 56, 58, 61, 103, 105and 152 can be provided with the coating 154. The coating 154 may alsoinclude other ingredients providing the catheter 10 with additionaladvantageous properties. For example, the coating 154 may include anantithrombogenic ingredient such as heparin or aspirin. Such a coating154 would not only inhibit platelet deposition but also the formation ofblood clots.

[0078] As previously noted, the characteristics of the heat exchangefluid 85 may also be of importance in a particular heat exchangeenvironment. Although the heat exchange fluid 85 may include variousliquids, it is believed that gases may provide the greatest temperaturedifferential with the body fluid. Particularly if this fluid includesblood, gases that are inert or otherwise compatible with the vascularsystem will be appreciated. Although several inert gases might fulfillthese requirements, carbon dioxide is used for the heat exchange fluid85 in a preferred embodiment of the invention.

[0079] A further embodiment of the catheter 10 is contemplated formaximizing the surface area available for heat exchange. As illustratedin FIGS. 10A and 10B, the catheter 10 can be formed with a distal end 45of the shaft 40 disposed in the natural configuration of a spiral orpigtail 172. The relatively large diameter of the pigtail 172facilitates heat exchange, but tends to deter from a low profile desirefor insertion. Under these circumstances, it may be advantageous toinsert the catheter 10 over a stylet or guidewire 174 in order tostraighten the pigtail 172 as illustrated in FIG. 10B.

[0080] Hyperthermia and hypothermia for selective regions of the bodycan also be achieved by placing in the body conduit, such as the carotidartery 25, a heat pipe 161 best illustrated in the schematic view ofFIG. 11. In this embodiment, the heat pipe 161 includes a distal end 163and proximal end 165. The distal end 163 is adapted to be placed withinthe body conduit, such as the carotid artery 25. The proximal end 165 ofthe heat pipe 161 is adapted to be connected to an external heat sink orcooler, such as a thermoelectric cooler 167 or water jacket 168. A wickstructure 170 is provided in the heat pipe 161 to facilitate a flow ofheat exchange fluid from the cooler 167 to the distal end 163.

[0081] In a process involving the heat pipe 161, illustrated in FIG. 12,the heat exchange fluid is moved from the proximal end 165 of the heatpipe 161 either by gravity or by capillary action of the wick structure170 to the distal end 163. At the distal end 163 of the heat pipe 161,heat is transferred from the body fluid, such as blood, to the heatexchange fluid in its liquid state. This heat exchange liquid absorbs aheat of vaporization as it passes into a vapor state in the heat pipe161. The heat exchange fluid in its vapor state creates a pressuregradient between the ends 163 and 165 of the heat pipe 161. Thispressure gradient causes the vapor to flow to the cooler 165 where it iscondensed giving up its latent heat of vaporization. The heat exchangefluid in its liquid state then passes back through the heat pipe 161through the wick structure 170 or by gravity. The passive heat exchangesystem provided by the heat pipe 161 is vacuum-tight and can be operatedwith a minimum amount of the heat exchange fluid.

[0082] Although the heat exchange catheter 10 will be advantageous inthe hyperthermic or hypothermic treatment of any portion of the body 12,it is believed that it will be particularly appreciated in thoseprocedures which can benefit from the hypothermic treatment of the brain18, such as the treatment of ischemic stroke and/or head trauma. Aspreviously noted in comments directed to FIG. 1, the catheter 10 can beinserted into the femoral artery in the groin 14 and directed throughthe aortic arch 23 into the common carotid artery 25. As illustrated inFIG. 13, the catheter 10 can then be moved into the region of thearterial branch 27 where it will encounter the external carotid artery30 and the internal carotid artery 32. Since the external carotid artery30 is directed primarily to the facial regions, it does not supply asignificant amount of blood to the brain 18. In contrast, the internalcarotid artery 32 is almost solely responsible for feeding the capillarybed of the brain 18. Based on these considerations, hypothermictreatment of the brain 18 is best addressed by cooling the blood in theinternal carotid artery 32 without wasting any of the cooling propertieson the external carotid artery 30. In a method associated with oneembodiment of the invention, the most distal of the balloons, such asthe balloon 56 in FIG. 13 is preferably positioned within the internalcarotid artery 32. The more proximal balloons 58 and 61 can be disposedalong the common carotid artery 25. This embodiment of the catheter 10and its associated method will achieve a higher degree of heat transferwithin the internal artery 32 than the external artery 30.

[0083] In another embodiment of the catheter 10 best illustrated in FIG.14, an occlusion balloon 175 is provided distally of the heat exchangeregion 47. In this embodiment, the occlusion balloon 175 will preferablybe inflatable through a separate lumen in the shaft 40. As the catheter10, approaches the carotid branch 27, the occlusion balloon 81 isdirected into the external carotid artery 30 and inflated in order to atleast partially occlude that artery. The remaining proximal balloons 56,58 and 61 in the heat exchange region 47 are left within the commoncarotid artery 25 to promote heat exchange with the blood flowing to thebranch 27. With the external artery 30 at least partially occluded, heattransfer occurs primarily with the blood flowing into the internalcarotid artery 32.

[0084] A further embodiment of the invention is illustrated in FIG. 15operatively disposed in the common carotid artery 25 and internalcarotid artery 32. In this case, the catheter 10 includes a balloon 181which is attached to the distal end of the shaft 40 and provided with aspiral configuration. More specifically, the balloon 181 may be formedfrom several individual balloons, as with the embodiment of FIG. 7, foras individual flutes 183 on the single balloon 181. In either case, theseparate balloons (such as the balloons 103, 105 of FIG. 7) or theflutes 183 are oriented in a spiral configuration around the axis 41 ofthe catheter 10. The shaft 40 can be provided with any of theconfigurations previously discussed such as the eccentric configurationof FIG. 6.

[0085] By providing the balloon 181 with a spiral configuration, heatexchange is enhanced by at least two of the factors previouslydiscussed. Notably, the surface area of contact is increased between theblood 31 flowing externally of the balloon 181 and the heat exchangefluid flowing internally of the balloon 181. The spiral configurationalso enhances the mixing properties of both the blood 31 and the heatexchange fluid 85.

[0086] As noted, the heat exchange fluid 85 may be cooled to a sub-zerotemperature. In order to thermally protect the internal lining of theartery 32 from direct contact with the subzero coolant, it may bedesirable to provide the tips of the flutes 183 with a thicker wall 185,as shown in FIG. 16. This thicker wall 185 might be advantageous in anyof the balloon configurations previously discussed, but would appear tobe most advantageous in the embodiments of FIG. 7 and 15 where thecontact with the artery 32 tends to be more localized by thelongitudinal balloons 103, 105 (FIG. 7) on the spiral flutes 183 (FIG.15).

[0087] Still a further embodiment of the invention is illustrated inFIG. 17. In this embodiment, the shaft 40 includes an inner tube 190disposed within an outer tube 192. These tubes 190, 192 may beconcentric and longitudingly movable relative to each other. The tubes190, 192 terminate respectively in manifolds 194, 196. Between thesemanifolds 194, 196, a multiplicity of hollow fibers 198 can be disposedat the distal end 45 to define the heat exchange region 47 of thecatheter 10. The hollow fibers 198 each include an internal lumen whichprovides fluid communication between the manifolds 194 and 196. Inoperation, the heat exchange fluid 85 flows distally along the innertube 190 into the distal manifold 194. From this manifold 194, the heatexchange fluid 85 flows into the internal lumens of the hollow fibers198 proximally to the proximal manifold 196. The warmer heat exchangefluid 85 flows proximally from the manifold 196 between the inner tube190 and outer tube 192.

[0088] Preferably, the hollow fibers 198 have a wall thickness that isthin enough to allow maximum heat transfer, yet strong enough towithstand the pressure requirements of the heat exchange fluid 85. Thehollow fibers 198 are further adapted to achieve ideal heat transfer bythe maximization of both surface area and coolant flow. The smaller thediameter of the fibers 198, the more fibers can be fit into the catheter10 with a corresponding increase in surface area. As the diameter of thefibers 198 is decreased, however, the resistance to fluid flow increasesthus lowering the coolant flow rate. The effect of the inflow andoutflow lumens must also be considered in determining the fluidresistance. Ideally, the wall thickness of the hollow fibers 198 is in arange between 0.00025 inches and 0.003 inches. In a preferred embodimentthe wall thickness is in a range between 0.00075 inches and 0.002inches, and ideally 0.00125 inches. The outer diameter of the hollowfibers 198 will typically be between 0.008 inches and 0.035 inches. In apreferred embodiment the outer diameter is in a range between 0.010inches and 0.018 inches, and ideally 0.015 inches.

[0089] It will be noted that the heat exchange fluid 85 flowing in theinner tube 190 is insulated in several respects from the blood streamoutside the catheter 10. This flow channel in the inner tube 190 isinsulated not only by the wall of the outer tube 192, but also by thecoolant returning in the flow channel associated with the outer tube192. The heat exchange fluid 85 in the inner tube is further insulatedby the thickness of the inner tube wall.

[0090] In the heat exchange region 47, the wall thicknesses associatedwith the inner tube 190 and the outer tube 192 is preferably reduced inorder to provide additional volume for the hollow fibers 198. With areduced wall thickness, the inner tube 190 also contributes to the heatexchange occurring in the region 47.

[0091] The hollow fibers 198 offer several advantages to this embodimentof the catheter 10. Notably, they provide a very high surface areabetween the blood 31 and the heat exchange fluid 85. This greatlyenhances the heat exchange characteristics of this embodiment.Countercurrent flow can also be maintained further facilitating the heatexchange capabilities of this catheter.

[0092] The hollow fibers 198 can be spiraled as illustrated in FIG. 18by twisting the inner tube 190 with respect to the outer tube 192. Thischaracteristic can be used to provide a shorter and lower profile heatexchange region 47 in order to facilitate introduction of the catheter10. A lower profile may also be obtained by separating the manifolds 194and 196 a distance substantially equal to the length of the fibers 198.This will tend to hold the fibers in a straight, parallel relationshipand thereby facilitate introduction of the catheter 10. The spiraledconfiguration of the hollow fibers 198 can be maintained during heatexchange in order to further increase the heat exchange area per unitlength of the catheter 10. Alternatively, the fibers 198 can bepositioned to loosely float and undulate between the manifolds 194 and196 as illustrated in FIG. 19. This characteristic of the fibers 198will not only provide the increased heat exchange area desired, but alsopromote mixing within the blood 31.

[0093] The fibers 198 will typically be formed of common materials suchas polyolefin nylon and polyurethane. The fibers can be coated with aclot-inhibiting material such as heparin. Other materials advantageousfor inhibiting the formation of blood clots might include those whichform polymer surfaces with 16 or 18 carbon alkyl chains. These materialsattract albumin and thereby inhibit clot formation. In a furtherembodiment, the fibers 198 can be provided with micropores which permitthe leaching of such clot inhibiting pharmaceuticals as heparinizedsaline which could also serve as the heat exchange fluid 85.

[0094] The embodiment of FIG. 20 also takes advantage of the significantheat exchange characteristics associated with the hollow fibers 198. Inthis embodiment, the manifold 194 at the distal end 45 of the catheter10 includes a potting seal 201 with a distal surface 203. The fibers 198are held in the potting seal 201 with the lumens of the fibers 198exposed at the surface 203. The distal end of the inner tube 190 is alsoheld in the potting seal 201 with its lumen exposed at the distalsurface 203. In this embodiment, the manifold 194 includes a cap 205which may have a hemisphere configuration. This cap extends over thedistal surface 203 of the potting seal 201 and provides fluidcommunication between the lumen of the inner tube 190 and the lumens ofthe hollow fibers 198. This cap 205 may also be constructed of materialsand wall thicknesses that insulate the blood vessels from potentialcontact with a cold catheter tip.

[0095]FIG. 21 illustrates in a cross-sectional view a first flow channel204 which extends along the lumen of the inner tube 190 and a secondflow channel 206 which extends along the lumen of the outer tube 192outwardly of the inner tube 190. As the heat exchange fluid 85 isintroduced into the first flow channel 204, its direction is reversed incap 205 so that the flow of the fluid 85 in the hollow fibers is counterto the flow of the body fluid, such as blood, in the body conduit, suchas the artery 32. After moving through the fibers 198, the heat exchangefluid 85 passes along the second flow channel 206 between the inner tube190 and outer tube 192, and exits the catheter 10 at the proximal end43.

[0096] The embodiment of FIG. 20 also includes a Y-connector 207disposed at the proximal end 43 of the catheter 10. This connector 207is shown in greater detail in the enlarged view of FIG. 22. In this viewit can be seen that the connector 207 includes a body 210 with screwthreads 212 at its distal end and screw threads 214 at its proximal end.At the distal end of the body 210, a screw cap 216 mates with the screwthreads 212 to engage an annular flange 218 at the proximal end of theouter tube 192. In this manner, the Y-connector 207 forms a seal withthe proximal end of the outer tube 192 and provides fluid communicationbetween the second flow channel 206 and a lumen 221 of the Y-connector207. A side port 223 communicates with this lumen 221 and provides anexit port for the secondary flow channel 206.

[0097] In order to prevent leakage from the lumen 221 at the proximalend 43 of the Y-connector 207, a releasable seal 225 can be formed atthe proximal end of the body 210. In the illustrated embodiment, thereleasable seal 225 includes a cap 227 which is threaded to registerwith the threads 214 of the body 210. This cap 227 extends around theproximal end of the body 210 and compresses an elastomeric washer 230against the body 210 and the outer surface of the inner tube 190. Bytightening the cap 227, the washer 230 is compressed to seal the lumen221. This compression also functions to inhibit, but not necessarilyprevent, axial movement between the outer tube 192 and inner tube 190.The releasability of the seal 225 can be appreciated in order tofacilitate this relative movement between the tubes 190 and 192 for thereasons previously discussed. This form of a releasable-seal 225 iscommonly referred to as a Tuohy-Borst seal.

[0098] The relative movement between the inner and outer tubes 190 and192, respectively, will be appreciated in order to provide the tubes 190and 192 with a first position wherein the fibers 198 have a low profileconfiguration as illustrated in FIG. 23. The relative movement will alsobe appreciated in order to provide the tubes 190 and 192 with a secondposition wherein the hollow fibers 198 form an increased profile asillustrated in FIG. 24. It can be appreciated that this profile willfacilitate heat exchange by providing an increased spacing of theindividual hollow fibers in the body fluid.

[0099] Another feature associated with these two positions isillustrated in FIG. 23 where the inner tube 190 is expanded in thicknessat its distal end in order to form a ramp or taper 232. In thisembodiment, the taper 232 is annular and extends radially outward withprogressive distal positions along the tube 190. As the inner tube 190is drawn proximally relative to the outer tube 192, the taper 232 isbrought into sealing engagement with the proximal end of the hollowfibers 198 and potting seal 201. This effectively seals the distal endof the outer tube 192 against the outer surface of inner tube 190, andprohibits any loss of the heat exchange fluid 85 between the inner andouter tubes 190 and 192 at the distal end 45.

[0100] This loss of the heat exchange fluid 85 can also be addressedwith a seal tube 234 which can be positioned between the inner and outertubes 190, 192 and inwardly of the hollow fibers 198. In thisembodiment, a distal end 236 of the seal tube 234 is generallycoextensive with the distal end of the outer tube 192. The seal tube 234is preferably provided with an inner diameter greater than the outerdiameter of the inner tube 190. As a result, the inner tube 190 is freeto move relative to the outer tube 192 to achieve the advantagespreviously discussed. However, when the inner tube 190 is drawnsufficiently proximal of the outer tube 192, the taper 232 will contactthe distal end 236 of the seal tube 234. This effectively forms the sealbetween the inner and outer tubes 190 and 192, respectively at thedistal end of the outer tube 192. With the taper 232 wedged against theseal tube 234, the fibers 198 are maintained in their operativefree-floating configuration as illustrated in FIG. 24.

[0101] Alternatively, a non-tapered inner tube 190, can be mated with aclosely fitted seal tube 234. With very small and controlled differencesbetween the outside diameter of the inner tube 190 and the insidediameter of the seal tube 234, for example 0.0005 to 0.003 inches, aneffective seal can be constructed without the taper 232. This embodimentrelies on the length of the seal tube 234, the surface tension of thecoolant fluid 85, and the small capillary gap to create a resistancegreater than the pressure of the coolant fluid during operation. Thisdesign does not require the inner tube to be moved a fixed distancerelative to the outer tube and does not require a constant tensionbetween the inner and outer tubes to effect a seal.

[0102] The seal tube 234 is preferably constructed of polyimide whichallows for a precision and constant inner diameter. In addition,polyimide is available in very thin wall thicknesses so that the sealtube 234 will not occupy a significant portion of the annular spacewhich is more appropriately dedicated to the fibers 198.

[0103] A method for manufacturing the hollow fiber embodiments of thecatheter 10 is illustrated in FIGS. 25-27. In FIG. 25, a planar mat 241of the hollow fibers 198 is formed with a generally planarconfiguration. In this mat 241, the fibers 198 are oriented in agenerally parallel configuration with angled potting seals 201 and 243formed at opposite ends of the fibers 198. This fiber mat 241 can berolled onto the outer surfaces of the inner tube 190 and seal tube 234as illustrated in FIG. 26. In this step, the potting seal 201 is formedaround the distal end of the inner tube 190 while the potting seal 243is formed around the distal end of the seal tube 234.

[0104] By initially forming the fibers 198 into the mat 241, a generallyuniform thickness of the mat 241 can be maintained. Rolling the mat 241onto the tubes 190 and 234 maintains this uniform thickness and alsofacilitates orientation of the fibers 198 onto the cylindrical tubes 190and 234. This technique also forms an inwardly spiraling helical bondjoint profile that aids in directing the blood flow in order to inhibitclot formation by preventing stagnant blood flow areas at the bondjoint. With the potting seals 201 and 243 suitably bonded to the tubes190 and 234, respectively, the cap 205 can be mounted over the distalend of the fibers 198 as previously discussed. At the proximal end ofthe fibers 198, the seal tube 234 can be mounted in the distal end ofthe outer tube 192 as illustrated in FIG. 27.

[0105] The seal tube 234 offers some interesting possibilities for theinfusion of fluids at the distal end 45 of the catheter 10. Of course,it is always possible to provide an additional lumen within the shaft ofthe catheter 10. In such an embodiment, the fluid to be infused could beinjected into the additional lumen at the proximal end 43 to exit thecatheter at the distal end 45. Alternatively, the fluid to be infusedmight be included in the heat exchange fluid 85. The tolerance betweenthe seal tube 234 and the outer diameter of the inner tube 190 couldthen be controlled to provide a calibrated leak of the heat exchangefluid 85 at the distal end 45 of the catheter 10. Micro holes might alsobe drilled into the outer tube 192 or inner tube 190 to provide for acontrolled leakage of the infusion fluid.

[0106] Each of the foregoing embodiments of the heat exchange catheter10 is adapted for use in cooling the entire human body, or perhaps onlya portion of the total body. Methods of operation will vary widelydepending on the focus of a particular procedure. By way of example, itwill be noted with reference to FIG. 28 that the catheter 10 isparticularly adapted for cooling blood in a procedure which may involveas many as three of the catheters 10. In FIG. 28, a human body 245 isillustrated along with a portion of the blood circulatory systemincluding a pair of femoral veins 247, 250 and a subclavian vein 252.These veins 247, 250 and 252 all extend into the vena cava 254 of thebody 245. In this procedure, separate catheters, such as the heatexchange catheter 10, can be introduced into each of the femoral veins247, 250 and the subclavian vein 252 with their respective heat exchangeregions disposed in the vena cava 254. Alternatively, and preferably,only two such catheters would be introduced from two of the three veins247, 250 and 252.

[0107] A systemic version of the catheter might have a diameter in arange of between 9 and 15 French, and a length of approximately 20 to 80centimeters long. It is contemplated that this design could conceivablycool the body in several hours. The use of two such catheters insertedinto the vena cava 254 as mentioned above could be expected to reducethe time required to cool the body by a factor of 2. It will beappreciated that similar catheters and methods can be used to lower thetemperature of blood in the native carotid or in the vertebralcirculatory system. The amount of blood heat lost is directlyproportional to the temperature differential, the blood velocity and theblood-to-catheter surface area.

[0108] Particularly in an operative setting wherein the heat exchangecatheter 10 is to be inserted into a blood vessel, a further designfeature best illustrated in FIGS. 29-33 will be of particular interest.In these views, an introducer 256 is positioned for percutaneousinsertion into a blood vessel such as the femoral vein 250. A sleeve 258is provided on the catheter 10 and slidable along the outer tube 192between two positions. The first position is illustrated in FIG. 29wherein the sleeve 258 is disposed in a spaced relationship with theheat exchange region 47. The second position of the sleeve 258 isillustrated in FIG. 30 where the sleeve 258 covers the heat exchangeregion 47. In this position the balloons or fibers associated with theregion 47 are compressed to a low profile state greatly facilitatingintroduction of the catheter 10 into the introducer 256. In addition,the covered heat exchange region 47 is stiffened for easier introductioninto the introducer 256. The fibers and/or balloons are also protectedfrom the interior surface of the introducer 256. Optionally, astiffening mandril may be inserted down one or more of the tubes 190,192 to facilitate introduction of the catheter 10 into the introducer256.

[0109] After this initial insertion, the sleeve 258 remains within theintroducer 256 while the remainder of the heat exchange region 47 ismoved distally into the conduit as illustrated in FIG. 31. At thispoint, the sleeve 258 can be removed from the introducer 256 by slidingit proximally to its first position as illustrated in FIG. 33.

[0110] This method of introduction is facilitated by providing thesleeve 258 with a generally Cylindrical configuration. The diameter ofthe cylindrical sheath should be less that the inside diameter of theintroducer 256. However, at the proximal end of the sheath 258, anannular flange 261 or other enlargement can be provided to ensure thatthe sheath 258 does not pass beyond the introducer 256.

[0111] Another feature associated with the present invention relates toa blood clot basket or snare 263, best illustrated in FIGS. 34 and 35.This snare 263 is preferably positioned downstream of the heat exchangeregion 47 associated with the catheter 10. It being appreciated that anystructure disposed in a blood vessel may tend to generate blood clots,it is the purpose of the snare 263 to capture any such clots. The snare263 of the preferred embodiment includes a plurality of wires 265 whichextend along a shaft 267 with their opposing ends fixed in the manifold194 and a distal cap 270. The wires 265 in a preferred embodiment areformed of stainless steel or a nickel titanium alloy.

[0112] In the illustrated embodiment, the shaft 267 extends to theproximal end 43 of the catheter 10 either through the lumen of the innertube 190 or alternatively through a second, separate lumen in the innertube 190. In the former case, a seal would be required at the distal endof the manifold 194 to prevent any leakage of heat exchange fluid 85around the shaft 267.

[0113] In either case, the shaft 267 is free to move relative to theconcentric tubes 190 and 192. When the shaft 267 is moved relativelydistally, the snare wires 265 are provided with a generally low profile.When the shaft 267 is moved relatively proximally, the wires 265 deployto provide the snare with an enlarged high-profile configuration asillustrated in FIG. 35.

[0114] In a further embodiment of the snare 263, the wires 265 areconnected to the manifold 194 and extend to distal ends which areunattached or free. The wires 265 in this embodiment, best illustratedin FIG. 36, are bent to a deployed enlarged configuration. With such anembodiment, insertion is facilitated by providing a delivery sheathwhich is movable to maintain the wires 265 in a low-profile state. Oncethe catheter 10 is in place, the sheath 262 can be removed therebypermitting the wires 265 to automatically expand to their enlargedhigh-profile state.

[0115] With respect to the forgoing disclosure as a whole, it will beapparent that many variations from these preferred embodiments will nowbe apparent to those skilled in the art. For example, with respect tothe balloon embodiments previously discussed, it will be appreciatedthat the advantages of this invention can be derived with only a singleballoon. On the other hand, there seem to be several advantagesassociated with multiple balloon embodiments. Notably, a more even andbalanced transfer of heat exchange can be achieved with multipleballoons. In addition, there appears to be better mixing with respect toboth the blood 31 as well as the heat exchange fluid 85. Multipleballoons also provide an increased surface area relative to singleballoon embodiments. Furthermore, the overall flexibility of thecatheter 10 is enhanced with multiple balloons separated byinterruptions which provide natural flex points for the catheter. Whenthe balloons experience the high perfusion pressure, they become morestiff. The reduced diameter interruptions provide for increasedflexibility at these joints.

[0116] Additional flexibility can be derived by providing the shaft 40with variable stiffness. This variability can be produced by differentmaterials forming the shaft 40 along its length or alteratively,tapering or otherwise varying the diameter of the shaft 40. For example,the shaft 40 can be progressively tapered from its proximal end 43 toits distal end 45 in order to provide a softer and more flexible heatexchange region 47.

[0117] In any of the foregoing embodiments of the catheter 10, the innertube 190 can be provided with a central lumen facilitating introductionover a guidewire and providing a capability for the infusion of fluidsthrough the catheter 10.

[0118] With the intent of maximizing heat transfer with the body fluidin a conduit feeding a specific region of the body, any of the factorspreviously noted can be addressed to provide structural modifications tothe foregoing embodiments. Of course changes in the material or size ofany of the structural elements described can be varied to achievevarious heat exchange properties. Realizing the many changes which mightbe contemplated, one is cautioned not to limit this concept only to thespecific embodiments illustrated and disclosed, but rather to determinethe scope of the invention with reference to the following claims.

1. A catheter having an elongate configuration with a proximal end and adistal end, the catheter comprising: an outer tube having an elongateconfiguration and a first lumen; an inner tube disposed in the firstlumen of the outer tube and having a second lumen extending between theproximal end and the distal end of the catheter; portions of the innertube defining a first fluid flow path extending along the second lumenbetween the proximal end and the distal end of the catheter; portions ofthe outer tube and the inner tube defining a second flow path extendingbetween the first tube and the second tube; and a plurality of hollowfibers providing fluid communication between the first fluid flow pathand the second fluid flow path.
 2. The catheter recited in claim 1,wherein: each of the hollow fibers has a proximal end and a distal end;the distal end of each of the hollow fibers has a fixed relationshipwith the distal end of the inner tube; and the proximal end of each ofthe hollow fibers has a fixed relationship with the distal end of theouter tube.
 3. The catheter recited in claim 2, wherein the inner tubehas properties for moving relative to the outer tube to vary theconfiguration of the hollow fibers extending between the inner tube andthe outer tube.
 4. The catheter recited in claim 3, wherein: portions ofthe inner tube define a taper, the inner tube being axially movable tobring the portions of the inner tube into sealing proximity with thehollow fibers.
 5. The catheter recited in claim 1 further comprising: acap disposed over the distal ends of the inner tube and the hollowfibers.
 6. The catheter recited in claim 1, further comprising: a sealtube disposed inwardly of the proximal end of the hollow fibers andforming a seal with the distal end of the outer tube and the proximalends of the hollow fibers.
 7. The catheter recited in claim 6, whereinthe seal tube extends proximally of the proximal end of the hollowfibers.
 8. The catheter recited in claim 4, further comprising: a sealtube disposed inwardly of the proximal end of the hollow fibers andforming a seal with the distal end of the outer tube and the proximalend of the hollow fibers; and the portions of the inner tube whichdefine the taper are axially movable relative to the outer tube in thesealing engagement with the hollow fibers.
 9. The catheter recited inclaim 1, wherein the hollow fibers are adapted to receive a heatexchange fluid from the first flow path and to release the heat exchangefluid into the second flow path.
 10. The catheter recited in claim 3,further comprising: a seal tube disposed between the hollow fibers andthe inner tube and having an inner diameter greater than the outerdiameter of the inner tube, but sufficiently close to the outer diameterof the inner tube to form a liquid seal between the seal tube and theinner tube by capillary action.
 11. The catheter recited in claim 10,wherein: portions of the inner tube define a taper, the inner tube beingaxially movable to bring the portions of the inner tube into sealingproximity with the distal end of the seal tube.
 12. The catheter recitedin claim 5, further comprising: a coating of insulation covering the capat the distal end of the catheter.
 13. The catheter recited in claim 1,wherein the hollow fibers are adapted to receive a heat exchange fluidfrom the second flow path and to release the heat exchange fluid intothe first flow path.
 14. A method for making a heat exchange catheter,comprising the steps of: providing a first tube having a first lumenextending between a proximal end and a distal end; inserting a secondtube into the lumen of the first tube, the second tube having a secondlumen; connecting a plurality of hollow fibers in fluid communicationwith a first flow path extending along the second lumen of the secondtube, and a second flow path extending along the first lumen of thefirst tube outwardly to the second tube; and insuring that the secondtube is at least one of axially and rotationally movable relative to thefirst tube to vary the configuration of the hollow fibers in order tofacilitate heat exchange with the heat exchange catheter.
 15. The methodrecited in claim 14, wherein the insuring step includes the steps of:moving the second tube distally relative to the first tube to change thehollow fibers to a low profile state; and moving the second tubeproximally relative to the first tube to change the hollow fibers to ahigh profile state.
 16. The method recited in claim 14, wherein theconnecting step further comprises the steps of: forming the hollowfibers in a stack having a generally planar configuration; wrapping thehollow fibers stack around the second tube; and inserting the hollowfibers into the distal end of the first tube.
 17. The method recited inclaim 14, further comprising the steps of: fixing to the proximal end ofthe first tube a Y-connector having fluid communication with the secondflow path.
 18. The method recited in claim 17, further comprising thesteps of: attaching a locking device to the Y-connector, the lockingdevice being operable between a first position permitting movement ofthe second tube relative to the first tube, and a second positioninhibiting movement of the second tube relative to the first tube. 19.The method recited in claim 16, further comprising the step of: pottingthe hollow fiber stack to form an end seal tapered radially inwardly toinhibit formation of stagnant flow regions around the fibers of thestack.
 20. A method for operating a heat exchange catheter within a bodyconduit containing a body fluid, the method comprising the steps of:inserting into the body conduit the heat exchange catheter with an innertube disposed within an outer tube to define a first flow pathinteriorly of the inner tube and a second flow path between the innertube and the outer tube, and a plurality of hollow fibers disposed influid communication between the first flow path and the second flowpath; and creating a flow of heat exchange fluid by introducing the heatexchange fluid into one of the first flow path and the second flow path.21. The method recited in claim 20, wherein the inserting step includesthe step of pushing the inner tube distally relative to the outer tubeto provide the hollow fibers with a lower profile.
 22. The methodrecited in claim 20, wherein the creating step further comprises thestep of reciprocating the inner tube relative to the outer tube tocreate a continuous movement of the hollow fibers in order to facilitateheat exchange between the hollow fibers and the body fluid.
 23. Themethod recited in claim 20, further comprising the steps of: removingthe catheter from the body conduit, and prior to the removing step,pushing the inner tube distally relative to the outer tube to providethe hollow fibers with a lower profile.
 24. The method recited in claim20, wherein prior to the inserting step the method comprises the stepsof: providing a sheath outwardly of the outer tube and movable between afirst position spaced from the hollow fibers and a second positionproximate to the hollow fibers; and moving the sheath to the secondposition and over the hollow fibers to maintain the fibers in a lowprofile state.
 25. The method recited in claim 24, further comprisingthe steps of after the inserting step, moving the sheath from the secondposition to the first position.
 26. The method recited in claim 25,further comprising the step of after the first moving step, moving thesheath from the first position to the second position and withdrawingthe catheter.
 27. The method recited in claim 20, wherein the heatexchange fluid is a cooling fluid.
 28. A heat exchange catheter,including: an elongate shaft extending along an axis between a proximalend a distal end; first portions of the shaft defining an inlet lumenextending between the proximal end and the distal end of the shaft;second portions of the shaft defining an outlet lumen; a first manifoldin fluid communication with the inlet lumen at the distal end of theshaft; a second manifold in fluid communication with the outlet lumen ofthe shaft; a plurality of hollow fibers disposed to extend between thefirst manifold and the second manifold in fluid communication with theinlet lumen and the outlet lumen; and the catheter being adapted toreceive a heat exchange fluid at the proximal end of the inlet lumen,and to direct the heat exchange fluid through the hollow fibers toexchange heat through the hollow fibers.
 29. The heat exchange catheterrecited in claim 28, wherein the first manifold is disposed distally ofthe second manifold.
 30. The heat exchange catheter recited in claim 29,wherein the outlet lumen is disposed outwardly of the inlet lumen. 31.The heat exchange catheter recited in claim 28, wherein the shaftcomprises: an inner tube defining the input lumen; and an output tubeconcentric with the input tube and defining with the input tube theoutput lumen.
 32. The heat exchange catheter recited in claim 31,wherein: the first tube has a fixed relationship with the firstmanifold; the second tube has a fixed relationship with the secondmanifold; and the first tube is axially movable relative to the secondtube to vary the configuration of the hollow fibers.
 33. The heatexchange catheter recited in claim 32, wherein the first tube is movableaxially of the second tube to separate the first manifold and the secondmanifold, and to place the hollow fibers in a generally straight,parallel relationship.
 34. The heat exchange catheter recited in claim28, wherein the heat exchange fluid is a liquid.
 35. A catheter adaptedto exchange heat with a body fluid flowing through a body conduit, thecatheter comprising: a shaft having an axis extending between a proximalend and a distal end, the shaft having an input lumen and an outputlumen; a plurality of hollow fibers defining a heat exchange region ofthe shaft and collectively defining an outer surface of the heatexchange region; the input lumen of the shaft coupled to the hollowfibers of the heat exchange region at a first location, the output lumenof the shaft being coupled to the hollow fibers of the heat exchangeregion at a second location such that a heat exchange fluid introducedinto the input lumen will enter the hollow fibers of the heat exchangeregion at the first location and will exit the hollow fibers of the heatexchange region at the second location through the output lumen.
 36. Thecatheter recited in claim 35, wherein the body fluid flows in a firstdirection through a body conduit and the heat exchange fluid flowsthrough the hollow fibers in a second direction opposite to the firstdirection.
 37. The catheter recited in claim 35, further comprising: aclot inhibiting coating covering the hollow fibers.
 38. The catheterrecited in claim 36, further comprising: a clot snare disposed in thefirst direction from the heat exchange region.
 39. The catheter recitedin claim 37, wherein portions of each hollow fiber defines amultiplicity of micro pores and the coating is formed by a clotinhibiting chemical included in the heat exchange fluid and leechablethrough the micro pores of the fibers.
 40. A method for exchanging heatwith a body fluid in a body conduit, comprising the steps of:introducing into the body conduit a catheter having an inlet lumen andan outlet lumen; providing the catheter with a first cavity in heattransfer relationship with a body fluid in the body conduit; introducinga heat exchange fluid into the inlet lumen and into the first cavity;exchanging heat between the heat exchange fluid and the body fluid inthe body conduit; removing the heat exchange fluid from the first cavitythrough the outlet lumen; and during the providing step, providing thecatheter with a plurality of hollow heat exchange fibers each extendingin fluid communication with the inlet lumen and the outlet lumen, theheat exchange fibers collectively defining the first cavity in heattransfer relationship with the body fluid in the body conduit.
 41. Themethod recited in claim 40, wherein the second introducing step includesthe step of introducing the heat exchange fluid into the hollow fibers.42. A catheter having a elongate configuration with a proximal end anddistal end, comprising: an operative area of the catheter sized andconfigured for disposition in a vessel containing blood flowing in aparticular direction, the operative area being adapted to perform apredetermined function and the blood in the vessel having a tendency toform blood clots; and a snare disposed in the particular direction fromthe operative area and being operable from the proximal end of thecatheter to move from a low-profile state facilitating insertion of thecatheter into the vessel, and a high-profile state facilitating captureof any blood clots.
 43. The catheter recited in claim 42, wherein thesnare is disposed distally of the operative area of the catheter. 44.The catheter recited in claim 42, wherein the operative area includes aheat exchange region of the catheter.
 45. The catheter recited in claim44, wherein the heat exchange region is a heat receiving region of thecatheter.
 46. The catheter recited in claim 42, wherein the snareincludes: a plurality of elongate filaments each having a first endattached to the operative region of the catheter and a second end. 47.The catheter recited in claim 46, wherein the second ends of thefilaments are unattached.
 48. The catheter recited in claim 46, wherein:the catheter further comprises a cap disposed at the distal end of thecatheter; the second ends of the filaments are attached to the cap; andmovement of the cap relative to the operative region of the catheterchanges the profile of the snare.
 49. The catheter recited in claim 48,further comprising: a shaft attached to the cap and extending to theproximal end of the catheter; whereby the profile of the snare ischanged by movement of the shaft relative to the operative region of thecatheter.
 50. The catheter recited in claim 42, wherein the filamentsare formed of wire.
 51. The catheter recited in claim 50, wherein thewire filaments include a nickel titanium alloy.
 52. A heat exchangecatheter having a elongate configuration and extending between aproximal end and a distal end, the catheter being adapted for coolingthe blood of a patient, comprising: a heat exchange region of thecatheter; a plurality of fibers included in the heat exchange region,with each of the fibers having a hollow configuration and being adaptedto receive a heat exchange fluid; and a coating disposed on the outersurface of the fibers to inhibit the formation of blood clots on thecooled fibers.
 53. The heat exchange catheter recited in claim 52,further comprising a chemical included in the coating and havingcharacteristics for inhibiting the formation of the blood clots.
 54. Theheat exchange catheter recited in claim 53, wherein the chemicalincludes heparin.
 55. The heat exchange catheter recited in claim 53,wherein: each of the fibers includes a multiplicity of micro poresextending between the hollow interior of the fibers and the outersurface of the fibers; and the chemical is included in the heat exchangefluid and leached with the heat exchange fluid through the micro poresto coat the outer surface of the fibers.
 56. The method recited in claim20 further comprising the step of: moving the inner tube relative to theouter tube to change the profile of the hollow fibers.
 57. The methodrecited in claim 20, wherein the creating step includes the step of:providing a heat exchange fluid in the form of a liquid.
 58. The methodrecited in claim 20, wherein the creating step includes the step of:providing a heat exchange fluid in the form a gas.
 59. The methodrecited in claim 20, wherein the creating step includes the step of:heating the heat exchange fluid prior to introducing the heat exchangefluid into the catheter.
 60. The method recited in claim 20, wherein thecreating step includes the step of: cooling the heat exchange fluidprior to introducing the fluid into the catheter.
 61. The heat exchangecatheter recited in claim 28, wherein the heat exchange fluid is a gas.62. The heat exchange catheter recited in claim 28, wherein the heatexchange fluid is a cooling fluid.
 63. The heat exchange catheterrecited in claim 28, wherein the heat exchange fluid is a heating fluid.